Method of insulating a metal structure and insulated metal structure



magnesia or mineral wool. structures are not only expensive, heavy, and

Patented Feb. 2, 1954 "UNIT ED "STATES IPA-TENT OFFICE METHOD OF INSULATING-A METAL; STRUC- TURE AND INSULATED .METAL STRUC- TURE John H. Baker, Bonanza, and-RoyE. Nelson, Salt Lake City, Utah, assignors. to. American Gilsonite Company,- Salt Lake City, .Utah, a corporation of Delaware No Drawing. Application July 6; 1951,

Serial No. 235,568

1 20.: Claim 1 I'his invention relates to insulation of the type that is, applied to structures to retard the fiow .of heat therefrom and also for the prevention of corrosion, and particularly refers to a method and product that may be applied to metallic structures of substantially any nature, but more specifically to those that are buried in the earth, for-example pipes or conduits that are conveying heated fluids.

Heretofore ithas been the practice to protect,

structures of. various kinds and particularly underground piping systems, and specifically those which are adapted to convey steam or other heated fluids, against loss of heat and also against corrosion from soil waters, by enclosing them'in :laminated wrappings of felt or asbestos bound together and to the pipe by melted enamel, tar,

asphalt and the like, or by supporting them in .water-tight concentric casings of steel, terracotta or concrete and filling the annulus with These composite time-consuming to fabricate but introduce other complications by requiring frequent maintenance and, if they are placed underground, call for .large'and deep trenches, drainage systems are similar undesirable features.

invention comprehends broadly an improved thermal loss retarding and corrosion preventing body which can be conveniently termed insulation, together with a novel method of form- ,ing the. same from a finely divided mass of one onmoreof thenatural asphaltite groupof bi- ..tuminous materialsincluding gilsonite, glance pitch and grahamite. These are essentially nat- .urallyoccurring hydrocarbons having softening points (ring and ball,- pressed powder) between about 275 and 400 F. with a few examples fusing as high as 600 F. Certain members of the natural asphaltic pyrobitumens, notably vurtzilite, .andcertain elaterites may be heat treated to undergo. ,-partial depolymerization so as to have a softening point in the upper portion of the temperature ranges given above,and hence are ,usefulin this method.

The material is first ground to a powdered vcondition, .desirably so that about'50 to 30 per cent. or more .will. passa 10. mesh screen, although the presence of larger pieces, up to about 1. inch inmaximum, dimension, isnot objection-,3 able. A, considerable proportion of exceedingly fine,. mat erial, of the nature of an impalpable ,powden-or dust is;; not; objectionable. I;his:-,is zpl ced;;. n-,contact with the-struc ur tube ;isulateditc. a-thidsnmaoiabout 2.1110,. 5 inche iand the structure is then heated, as by steam, hot

gases, an-electric current or the like, to a temrperature depending somewhat onits subsequent to form a continuous length,- which-iscentered and supported temporarily in the trench at a distance of about 2 to 5iinches above the bottom.

'-='The finely divided gilsonite, for example, is poured into theditch, filling-the spacearound the sides soil water.

.and bottom of the pipe and covering the top to a thickness of about 2 to 5 inches. 2

The earth is then backfilled over the covered pipe, taking reasonable care not to disturb the gilsonite layer.

.When' the desired length of underground pipe section is thus covered, steam or another source of heat is passed through the pipe to raise its surface temperaturewithin the range of about 235 to about 375--lt., for aperiod of about 10 ,to; 50 hours or more,- depending upon the nature of the 'material used and the severity of the temperature and corrosion conditions. That portion of the pulverized material in contact with the pipe surface will fuse together and to the surface relatively quickly to form a dense glassy layer which grades outwardly into a differentially ..sintered zone surrounded by the completely un- 35 where the heat from the pipe has not been able bondedor discreteparticles at that distance to travel. Thiscompletes the formation of the .insu1ation,;-as will be'discussed in further-detail .below.

It has been found that the asphaltite group,

.and particularly gilsonite in finely divided condition, is exceedingly hydrophobic, i. e.,- not at all'readily wet by liquid waterandparticularly In fact, although'its density is somewhatgreater thanwater, even relatively large lumps will float thereon due to the inherent rezpulsipn abetween the; gilsonite surface and the water surface. Tests of insulation on pipe coated as just described have shown the-hitherto unappreciated fact that even though there is no continuous layer-or skin ,onthe outside of the insulat o .r iqu dwate -wi ;;not,- penetrate t mass of discrete particles under, those hydrostatic 1 head vconditions; thata are-encountered in underround .-piping:.=systems.

Additionally, it has been found that the insulation formed by this procedure has a thermal conductivity both in completely dry and completely water-saturated and submerged soil, or about 0.03 to 0.04 B. t. 11. per hour per square foot per degree F. per foot of thickness, which is quite comparable to hitherto used dry insulating materials such as magnesia, asbestos felt and diatomaceous earth powder, all of which latter must be carefully protected against liquid water to be effective as insulation.

As a specific example, pulverized gilsonite from the Bonanza mine in eastern Utah, having a softening point of about 280 F. (ring and ball, pressed powder) and ground so that all of it passed through a mesh Tyler screen was placed in a 3 inch layer around a /2 inch pipe and the whole surrounded by sandy soil in a wooden box. The pipe was heated to a wall temperature of 260-270 F. for about 50 hours, at which time equilibrium conditions had been established.

The temperature gradients through the gilsonite insulation when the box was maintained at atmospheric temperature, measured by thermocouples located at the points indicated, are given below:

Temperature Differential in Insulation at Radial distances from pipe surface At the termination of the test, the fused gilsonite layer adjacent to the pipe surface was found to vary from about above the pipe to about twice that thickness below the pipe. From the completely fused zone at the pipe surface the sintering was progressively less for a short distance, merging imperceptibly to the loose. discrete particles which had been unchanged from their original condition.

These data indicate that beyond about one inch from the pipe surface the heat insulation characteristics become substantially constant.

When the soil surrounding the insulation was saturated with water and maintained submerged, and the pipe was allowed to cool and remain cold for several hundred hours and then heated, the temperature differentials noted were not substantially diiferent from the above table, indicating that the hydrophobic character of the unconsolidated or unbonded powdered material throughout the major and outer part of the insulation layer had effectively prevented infiltration of the water from the saturated soil.

Although the procedure and application outlined above is for the specific case of providing an effective heat loss and corrosion preventing insulation for a buried pipe, e. g., a pipe for underground use having a coating at least two inches thick comprising initially powdered gilsonite, it is obvious that, by suitable temporary forms and enclosures for the insulation, overhead lines and other structural configurations, for example fiat plates, complicated rolled and fabricated sections and the like can equally well be insulated, using suitably modified procedures and applicable materials from the group disclosed. Also, the thickness of the layer may be varied within wide limits depending. on the s ze of the structure to be protected, the economics of the heat loss that can be tolerated, and other factors that will be apparent to one skilled in this art. Accordingly, any variations and modifications of the precedure or applications to analogous or different environments that may fall within the scope of the appended claims are intended to be embraced thereby.

We claim:

1. A method of insulating a metal structure comprising covering a surface of said structure with a loose fill at least two inches in thickness consisting essentially of a pulverized material selected from the group consisting of gilsonite, glance pitch, grahamite, elaterite and wurtzilite, and heating said surface in contact with said fill to a temperature of about 200 F. to 500 F. to form said fill into an insulating body having a dense, fused first zone of said material immediately adjacent said metal surface, a second zone of sintered particles of said material merging into said first zone and extending outwardly therefrom, and a third zone of loose particles of said material merging into said second zone and extending outwardly therefrom.

2. The method of claim 1 wherein the pulverized material employed has a softening point (ring and ball, pressed powder) of about 275 F. to about 600 F.

3. The method of claim 1 wherein the pulverized material employed is pulverized gilsonite.

i. The method of claim 3 wherein the metal surface in contact with the loose fill of pulverized gilsonite is heated to a temperature of from about 235 F. to about 375 F.

5. The process of claim 3 wherein the metal surface in contact with the pulverized gilsonite is heated for about 10 to about 50 hours.

6. The process of claim 3 wherein the particle size of the pulverized gilsonite ranges in size from an impalpable dust up to about one inch in maximum diameter, with at least 50% thereof passing a 10 mesh screen.

7. A metal surface provided with an insulating body at least two inches in thickness consisting essentially of a material selected from the group consisting of gilsonite, glance pitch, grahamite, elaterite and wurtzilite, said body having a dense, fused first zone of said material immediately adjacent said surface, a second zone of sintered particles of said material merging into said first zone and extending outwardly therefrom, and a third zone of loose particles of said material merging into said second zone and extending outwardly therefrom.

8. An insulated metal surface as defined in claim 7 wherein the material of which the insulating body essentially consists has a softening point (ring and ball, pressed powder) between about 275 F. and 400 F.

9. An insulated metal surface as defined in claim 7 wherein the insulating body is about 2 to 5 inches thick.

10. An insulated metal surface as defined in claim 7 wherein the insulating body consists essentially of gilsonite.

11. An insulated metal surface as defined in claim 10 wherein the insulating body is about 2 to 5 inches thick.

12. A method of insulating an underground pipe comprising supporting a pipe spaced from the sides and bottom of a trench, surrounding said pipe in said trench with a loose fill at least 2 inches in thickness consisting essentially of pulverized material selected from the group-consisting of gilsonite, glance pitch, grahamite, elaterite and wurtzilite, and heating the outer surface of said pipe in contact with said fill to a temperature of about 200 F. to 500 F. to form said fill into an insulating body having a dense, fused first zone of said material immediately adjacent the outer surface of said pipe, a second zone of sintered particles of said material merging into said first zone and extending radially outward therefrom, and a third zone of loose particles of said material surrounding said sec ond zone.

13. The process of claim 12 wherein the pulverized material employed is pulverized gilsonite.

14. The process of claim 13 wherein the surface of the pipe in contact with the loose fill of pulverized gilsonite is from 2 to 5 inches thick.

15. The process of claim 13 wherein the surface of the pipe in contact with the loose fill of pulverized gilsonite is heated to a temperature of from about 235 F. to about 375 F.

16. The process of claim 14 wherein the surface of the pipe in contact with the loose fill of particulate gilsonite is heated for a period of about 10 to 50 hours.

17. The process of claim 13 wherein the particles of pulverized gilsonite range in size from a fine powder up to about one inch in maximum dimension, with about 50% to 80% passing a 10 mesh screen, and wherein the surface of said pipe in contact with said gilsonite is heated to a temperature of from about 235 F. to about 375 F.

18. An insulated underground pipe structure comprising a pipe, supported in and spaced from the sides and bottom of a trench in the ground, and an insulating body at least two inches in thickness surrounding said pipe, said body consisting essentially of a material selected from the group consisting of gilsonite, glance pitch, grahamite, elaterite and wurtzilite, and having a dense, fused first zone of said material im- "mediately adjacent the outer surface of said pipe,

a second zone of sintered particles of said material merging into said first zone and extending radially outward therefrom, and a third zone of loose particles of said material surrounding said second zone.

19. An insulated underground pipe structure as recited in claim 18 wherein the insulating body consists essentially of gilsonite.

20. An insulated underground pipe structure as recited in claim 19 wherein the insulating body is 2 to 5 inches thick.

JOHN H. BAKER. ROY E. NELSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,736,915 Illemann et al Nov. 26, 1929 2,061,825 Bly Nov. 24, 1936 

12. A METHOD OF INSULATING AN UNDERGROUND PIPE COMPRISING SUPPORTING A PIPE SPACED FROM THE SIDES AND BOTTOM OF A TRENCH, SURROUNDING SAID PIPE IN SAID TRENCH WITH A LOOSE FILL AT LEAST 2 INCHES IN THICKNESS CONSISTING ESSENTIALLY OF PULVERIZED MATERIAL SELECTED FROM THE GROUP CONSISTING OF GILSONITE, GLANCE PITCH, GRAHAMITE, ELATERITE AND WURTZILITE, AND HEATING THE OUTER SURFACE OF SAID PIPE IN CONTACT WITH SAID FILL TO A TEMPERATURE OF ABOUT 200* F. TO 500* F. TO FORM SAID FILL INTO AN INSULATING BODY HAVING A DENSE, FUSED FIRST ZONE OF SAID MATERIAL IMMEDIATELY ADJACENT TO OUTER SURFACE OF SAID PIPE, A SECOND ZONE OF SINTERED PARTICLES OF SAID MATERIAL MERGING INTO SIAD FIRST ZONE AND EXTENDING RADIALLY OUTWARD THEREFORM, AND A THIRD ZONE OF LOOSE PARTICLES OF SAID MATERIAL SURROUNDING SAID SECOND ZONE. 